Structural collapse of a freestyle ski-jump

During the morning completion works on a ski-jump and before the re-opening of an annual sporting event on the second day, attended then by thousands of visitors, the jump’s landing ramp collapsed. Fortunately, nobody was injured; however, the event had to be cancelled with the concomitant financial losses. Due to the high risk potential of the accident, an analysis of the failure was ordered by the public prosecutor. The key issue was not only to find the cause of the accident, but also to define precautions for future events.The landing ramp with a 20 m span was built up from framework units assembled by means of plug-and-socket connections. Based on the macroscopic appearance of the damage, the most probable primary fracture was determined. Analytical calculations showed that the primary broken connection’s lug was located in the most highly loaded area of the ramp. During the snow preparation, the static load in this area was more than twice the intended final load because of the unequal distribution of the snow. This critical load case had not been considered during the design of the ramp. Nevertheless, the collapse still could not be explained based on this fault, as the ultimate strength measured on undamaged specimens would still have been sufficient. Consequently, a reduced load capacity at the primary fracture had to be assumed. This hypothesis was supported by the fact that the crack proceeded through the welded seams rather than trough the parent material. By means of fractographical and EDX analysis, zinc was detected at the edge of the fracture surface. The metallographic findings precluded brittle fractures during the hot-dip galvanising as a reason for this anomaly. However, impermissible welding imperfections and insufficient corrosion protection were also found. The estimated load capacity of the thus reduced cross-section corresponded well with the assumed load at the time of the collapse.Based on the conclusions of this study, recommendations were derived regarding the design of the ramp (e.g. redundancy) and the welded construction, as well as the corrosion protection of the framework units.